Update some sim copyright headers to GPLv3-or-later

[Joel Brobecker]

> i.e. pediantically speaking, not aclocal depends on it, something in
> gdb depends on pkgconfig's pkg.m4.
> 
> If you want to get rid of this dependency, you can try to append
> pkg.m4 to an acinclude.m4 next to the configure.ac, which pulling in
> pkg.m4.

OK, that makes better sense to me. What still does not make sense
is why my run of aclocal does not produce the same result, though.
Either I'm missing something, and I would have expected aclocal
to complain, or the GDB sources is missing something, and we have
a bona fide issue.

-- 
Joel